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High Strain Dynamic Pile Testing

High strain dynamic pile testing is performed during pile installation to provide an estimation of pile capacity. The test is performed by attaching strain gages and accelerometers to the top of the pile. Signal from the gages are recorded by a pile driving analyzer (PDA). FTC utilizes a wireless communication system between the pile mounted gages and the PDA thereby eliminating the need for a main connecting cable. The wireless system allows for faster, more efficient testing and minimizes the chance for any testing delay associated with equipment damage.

It is also possible to efficiently perform PDA tests for several pile each day with one operator. All pile types including concrete, steel pipe pile or steel H-pile, auger cast pile or even drilled shafts can be tested with the PDA equipment.

PDA testing provides many advantages such as being able to confirm the geotechnical capacity of the pile during installation, and the ability for the operator to monitor efficiency of the pile driving hammer and pile stresses. PDA testing, when used as part of an overall geotechnical design program can allow for more efficient pile design (fewer or shorter pile compared with a higher factor of safety that may otherwise be warranted without PDA testing). The switch from allowable stress design to load and resistance factor design for federally funded and other projects has typically meant a greater amount of foundation testing. This is because the uncertainties associated with pile capacity (soil resistance) are greater than the uncertainties associated with the structural capacity of the pile. The soil resistance can be better quantified by measuring the dynamic resistance and estimating the static resistance with the PDA during installation.

Related services that are available from FTC include wave equation analysis to assess hammer selection and pile drivability, CAPWAP analysis to provide refined signal wave matching and pile capacity estimation and hammer calibrations.

It is important for PDA testing to be performed with qualified and experienced staff. FTC has provided PDA services on some of the most important bridge projects in the region. FTC has highly qualified and experienced staff in the areas of foundation design and evaluation which enable us to provide our services in a highly efficient and responsive manner.

SPT Hammer Calibration

Provide your clients with accurate blow count data for use in geotechnical design. Better position your firm to provide drilling services for federally funded state highway and bridge projects.

SPT hammer calibration is performed using a specially instrumented drill rod connected to accelerometers and data processor (typically the same unit that is used for PDA data collection). FTC is able to perform hammer calibration during normal production drilling and sampling without delaying your crews and avoiding the need to “drill just to calibrate”. We can quickly mobilize to your job site(s) to perform this calibration. Alternatively, you may arrange to have multiple rigs calibrated by us in a single day by drilling at the same site. Our services are provided in accordance with applicable ASTM standards and you will receive full energy transfer ratio (efficiency) statistical analysis and plots as part of the report for each hammer calibration.

Per ASTM D4633 hammer calibrations should be performed annually or more frequently based upon quality assurance requirements, rig and hammer maintenance intervals and prior to the start of major critical projects. Most companies run rigs with SPT auto hammers. Such hammers are typically far more efficient than 60 percent when properly functioning so you could design with corrected (typically higher) blow count data by knowing your hammer efficiency. Hammer calibrations can also reveal potential problems with your hammer system if abnormally low efficiencies are recorded that could then be addressed through repair and maintenance.